1. Field of the Invention
This invention generally relates to a thermal printer for printing an image, such as a character and symbol, by applying a heat pattern of an image to be printed to a recording medium, and, in particular, to a transfer type thermal printer in which a heatsensitive ink ribbon is used to transfer ink in the form of a desired heat pattern applied by a thermal printhead to a recording medium.
2. Description of the Prior Art
A transfer type thermal printer is well known in the art. In such a printer, a heatsensitive ink ribbon is placed as sandwiched between a recording medium, typically plain paper, and a thermal printhead, and, according to a heat pattern created on the thermal printhead in accordance with an image signal supplied thereto, the ink on the ink ribbon is selectively melted and transferred to the recording medium thereby forming a printed image on the recoding medium by the transferred ink. Such a transfer type thermal printer has numerous advantages, including capability of providing a printed image of excellent quality, high printing speed and quiet operation. Accordingly, it has been and is being actively applied as an output device of computer and/or wordprocessor system, or as a recording section of facsimile machine.
An ink ribbon or sheet used in such a transfer type thermal printer includes a base of thin resin film, paper or the like and an ink layer formed on the base. When manufacturing such an ink ribbon, the ink is first applied to the base as being heated to be in a melted condition and then it is cooled to the room temperature to solidify. The ink forming the ink layer is thus in a solid state at room temperature, and, thus, the ink is not transferred to any object even if it is brought into contact therewith. On the other hand, if the ink is heated above a predetermined temperature, it melts and becomes easily transferred to an object which is brought into contact therewith.
The thermal printhead contacts the ink ribbon at its base side so that a heat pattern created by the thermal printhead is applied to the ink layer as conducted through the base. Thus, in order to maintain a high printing speed and to reduce energy consumption, it is desirous to make the base of ink ribbon as thin as practically possible thereby allowing to increase the rate of heat transfer to the ink layer through the base under a given condition. Since the ink layer itself is already substantially thin, when the base is made thinner, the entier ink ribbon is made thinner. For this reason, extremely thin heatsensitive ink ribbons have recently become commercially available.
However, in prior art transfer type thermal printers, it has been noted a difficulty in setting such a heatsensitive ink ribbon ready for operation. It is more often than not that the ink ribbon becomes creased or twisted while it is being set in position, which could then cause malfunctioning in ink ribbon feeding operation and/or printed image of poor quality. Moreover, in such prior art printers, when the ink ribbon jams during operation, it is not easy to remove a sheet of recording paper on which printing has been carried out from the printer and the ink ribbon could be easily damaged while this sheet of recording paper is being removed. Thus, if such jamming occurs in a prior art printer, it could be rectified only with a great difficulty.